Fixes Issue #12268 for the io module - File readline, readlines and

Fixes Issue #12268 for the io module - File readline, readlines and
read or readall methods no longer lose data when an underlying read
system call is interrupted within an io module object.  IOError is no
longer raised due to a read system call returning EINTR from within
these methods.

This is a backport of changeset 781b95159954 from 3.2.
The earlier 2.7 changeset 67dc99a989cd already fixed this for the
builtin python 2.x file object.